My University just build this amazing library exclusively for the engineering departments and similar fields of study. This is my first time taking advantage of the new complex and I am sitting on the 3nd floor over an all glass-wall window. As the sun was setting I notice tiny popping noises on the windows: as if somebody was throwing a small pebbles. Because of the correlation between sunrise and sunset, my conclusion is that the only source of these "popping" noises are due to thermal expansion and contraction on the metal keeping the glass walls in place. I was also considering forces due to aerodynamic loads, but these are occurring sporadically with sometimes large time intervals. For those with structural engineering experience, what could be other causes? I feel like hearing the thermal expansion and contraction shouldnt create so much noise on a new "well build" building.